The present invention is directed generally towards the inspection of boreholes and other limited access passageways, and more particularly, to an inspection instrument having a low voltage, low power light-head and camera arrangement for capturing video images.
In drilling oil and gas wells it is often necessary to obtain information concerning conditions within the borehole. Where the borehole has casings and fittings, as is typical of production oil wells, there is a continuing need to inspect the casings and fittings for corrosion. The early detection of the onset of corrosion in borehole casings allows for the application of anti-corrosive compounds to the well. Early treatment of corrosive well conditions may prevent the need for expensive casing replacement procedures. Where the borehole may contain oil, natural gas, or water, it often proves convenient to verify the presence of these substances through visual examination.
There may also be a need to determine the entry points of fluids into a well. Where water is infiltrating an oil well, it is necessary to determine the point of entry so that steps may be taken to stop the infiltration. If a visual examination of a well bore reveals oil at one location and a mixture of oil and water at another location, it can be concluded that the infiltration of water is occurring at some point in between. By gradually moving a camera between the two locations, the point of infiltration may be located and consequently the flow of water may be blocked through subsequent action.
Although visual examination of well bores is highly desirable, the environmental conditions typical of oil and gas wells pose special problems that tend to hinder camera operation. Well bores range in depth from several hundred to several thousand feet. Consequently, hydrostatic pressure within a deep bore, in addition to high well head pressures caused by gas production, can be quite large and can reach and often exceed 70 mPa (10,000 pounds per square inch). Ambient well temperatures on the order of 135 degrees Celsius (275 degrees Fahrenheit) are not uncommon. In addition, oil wells typically contain highly corrosive hydrogen sulfide and carbon dioxide gases. These harsh environmental conditions dictate that cameras and associated lighting equipment must be enclosed within protective housings. Fluids collected in well bores further complicate the visualization problem. Collected fluids are generally dark, cloudy, and often contain mineral particulates in suspension. One effect most fluids found in well bores have is to reduce light transmission. For this reason, high intensity lights are generally required to illuminate a well bore sufficiently to obtain an adequate video image.
Prior devices for visually examining boreholes typically include a camera and a high intensity light source enclosed in a protective housing. The devices are generally attached to an armored cable that supports the device and provides electrical power and communication signals to the device. The cable is typically lowered and raised within the borehole by means of reel located at a surface station proximate the entrance to the borehole. The surface station further includes a power source and control apparatus for operation of the inspection device.
One constant problem facing down hole instrument designers is the need to make the instruments small enough to be usable in very narrow passageways, including those that have restrictions, such as small diameter pipes or casings but at the same time have the ability to provide high quality images, either in real time or stored for viewing later. Casings having internal restrictions, such as tubing, safety valves, or other devices, that result in an internal effective diameter of 44 millimeters (1xc2xe inches) are not uncommon. The need to provide both a camera and an associated light source can make the instrument too large to fit in such small diameter passageways.
Another problem faced by designers of borehole inspection devices is the effect of heat upon camera operation. Camera electronics possess a limited capacity to withstand heat and the combination of high ambient borehole temperatures and the heat generated by high intensity lighting systems may produce a temporary or permanent failure of the camera. Such failures can be quite expensive and time consuming as the instrument must either be raised until it cools down enough to once again come on line, or must be extracted from the borehole and replaced.
An example of an early borehole inspection device is one that includes a cylindrical housing into which is mounted a television camera and a light source in the form of a donut-shaped lamp that surrounds the television camera. The device also includes a coolant jacket and coolant that surrounds the heat sensitive camera electronics. Since the donut-shaped lamp surrounds the camera, heat developed by the lamp reaches the camera and will add to the heat environment the camera will experience. As discussed above, a level of heat that is too high will result in camera failure. The use of a cooling system in a down hole instrument is undesirable due to the added equipment that would be necessary, thereby increasing the size of the instrument, as well as the reliability considerations. The more equipment that is used, the more likely a failure will occur. Adding heat from a light source used to illuminate the field of view of the camera is also undesirable. Also, placing the lamp around the camera increases the diameter of the device thereby making it unusable in very restricted passageways. Approaches have been devised to longitudinally and physically separate the light source from the camera so that any heat developed by the light source will be generated at a distance from the camera. Once such approach is to mount the light source in front of the camera facing the field of view of the camera but separated from the camera by mounting arms. In this arrangement, the light source blocks a portion of the field of view of the camera, yet this approach has proven to be successful. In some applications however, is would be desirable to have a clear field of view for the camera.
A more modern borehole inspection device uses a back-lighted camera where the camera is suspended in front of a high intensity lamp and is axially separated from the lamp a sufficient distance to provide significant thermal isolation of the camera from the lamp. Light is directed into the camera""s field of view by means of a reflector located behind the camera. By isolating the camera from the light source heat, a significant improvement in the art has been provided and this approach has proven successful. A back-light arrangement separates the heat generated by the light source from the camera resulting in cooler temperatures for the camera.
However, because back-lighting is used, a brighter light source is needed with an accompanying higher power requirement. More electrical energy must be provided to the light source so that enough light reaches the camera""s field of view. Such increased power requirements either require a larger battery in the instrument, which can result in a larger and often impractical instrument, or power provided to the instrument through the cable which results in a larger cable. Additionally in this arrangement, the light source is exposed to the environment and must be sealed against contaminants, which is not a minor task. Further, the camera is extended from the light source by arms, which can be bent during operation. Bent arms can result in off-center view angles for the camera and if severe enough, the instrument must be withdrawn from the borehole and corrected.
Despite the above, the back-light approach has proven to be highly successful in large diameter tubular passageways. Better lighting is provided resulting in significantly better images. However, the back-light approach relies on the reflection of light from the walls of the passageway. In very small diameter passageways, the camera of the instrument has been found to be too large and it interferes with the needed reflection of light into the camera""s field of view. Insufficient light is therefore delivered and the results are not as desirable. A smaller instrument would be more useful.
Hence, those skilled in the art have recognized the need for an improved borehole inspection instrument that utilizes a low voltage, low power, high intensity light-head that is physically separated from the camera to reduce heat applied to the camera. Additionally, such a light source should be enclosed within the same housing as the camera thereby reducing the need to seal components of the instrument from down hole conditions. There is also a need to provide a light source that requires less electrical energy to generate enough light for the camera""s field of view. Further, a need has been recognized for a light source and camera arrangement wherein neither are mounted with arms. Yet further, a need has been recognized for a down hole instrument having a diameter small enough to fit within very small passageways, such as one with an effective diameter of 44 millimeters (1xc2xe inches). The present invention fulfills these and other needs.
Briefly and in general terms, the present invention is directed to an improved instrument for use in the inspection of boreholes. The inspection instrument comprises a camera and a light source arrangement. The light source is housed in the same housing or pressure barrel as the camera. An elliptical reflector is disposed about the light source to focus the light into an efficient light transmission system. The light transmission system forms an array about the camera to radiate light into the field of view of the camera. In a more detailed aspect, a shaped annular window is disposed in front of the light array to assist in dispersing the light from the array so that the illumination pattern is substantially coincident with the camera""s field of view. In another more detailed aspect, the light transmission system comprises the use of an optical fiber light transmission system. A plurality of optical fibers may be used to conduct the light from the light source to the array about the camera.
In accordance with another aspect, the camera and light source are separated from each other physically. This physical separation provides a degree of thermal insulation to the camera from heat generated by the light source. In a more detailed aspect, the camera is located at the distal end of the pressure barrel with the light source axially spaced proximally in relation to the camera a sufficient distance to thermally isolate the light source from the camera. The optical fibers forming an array of light sources about the camera do not generate any significant heat but provide a sufficient amount of light to fully illuminate the camera""s field of view. Because the light source array is approximately coplanar with the camera, a more efficient arrangement results. Disadvantages associated with backlighting the field of view, or with partially blocking the camera""s field of view with a light source disposed in front of the camera are nonexistent with this arrangement.
In another detailed aspect, the position of the light source and elliptical reflector is adjustable so that precise positioning of the light source for maximum light transfer to the optical fibers is possible. The light source is placed at a first focal point of the elliptical reflector and the optical fibers are placed at the second focal point which is removed from the first focal point.
In a further detailed aspect, a plurality of optical fibers are used to form the light array about the camera. These optical fibers are gathered into a single bundle and their proximal ends are positioned at the second focal point of the light source reflector for maximum light transfer from the light source to the optical fibers. The distal ends of the individual fibers that comprise the bundle are located at points spaced about the periphery of the camera on approximately the same plane as the camera lens. This arrangement provides for an unobstructed field of illumination of the fibers and an unobstructed field of view of the camera.
In one arrangement, the images produced by the light/camera system in accordance with aspects of the invention are communicated to the surface through electrical or optical conductors in the support cable for real-time viewing and processing at the surface. The images may also be recorded at the surface, as is common. Power may also be provided from the surface through the support cable to operate the camera and light source.
In yet another aspect of the invention, a power supply that is completely internal to the instrument may be used to supply power to both the camera and the light source due to the increased efficiency of the light source arrangement. In yet another aspect, standard size batteries may be used as that power source. In a further aspect, standard size D-cell batteries or Lithium batteries may be used.
In yet further aspects, an inspection instrument in accordance with the invention may contain an internal memory for the storage in digital form of the images created by the camera. The instrument may also include a programable processor for programmed operation of the camera. With this arrangement, the inspection instrument is capable of autonomous operation. It is programmed before introduction into the borehole to be inspected to capture a series of images at a predetermined time interval or intervals. The instrument remains in the borehole until its memory is full, the image program has been completed, or the batteries have been depleted. The instrument is then removed from the borehole and at the surface, the images are retrieved from the digital memory. Those images may then be processed at the surface.
Because of this efficient operation and the use of a self-contained battery system in this arrangement, the support cable can be of minimal size and the instrument is particularly adapted for use in small diameter passageways. No power conductors or data communication conductors are needed in the support cable. A much smaller and more prevalent cable commonly known as a xe2x80x9cslicklinexe2x80x9d may be used instead. A slickline is essentially a length of wire that is less expensive to operate and is far more available than electric line for field use. The need for surface support equipment is reduced (for example, no surface power supply is necessary) and the instrument is therefore more portable. The ability to run on a slickline results in an instrument that is usable in a much more diverse set of circumstances.